1. Field of the Invention
The present invention relates to a differential gear used for vehicles.
2. Description of the Prior Art
There are disclosed differential gears 301 and 303 and a driving power transmission device 305, respectively, as shown in FIGS. 1, 2 and 3 in Japanese Laid-Open Utility Model Publication No. 63-78746, Japanese Laid-Open Utility Model Publication No. 62-172842, and Japanese Laid-Open Patent Publication No. 3-239634.
Differential gears 301 and 303 include, respectively, bevel gear-type differential gear mechanisms 307 and 309, viscous couplings 311 and 313, and multiple disc clutches 315 and 317, and the driving power transmission device 305 includes a worm gear-type differential gear mechanism 319 and a viscous coupling 321.
Viscous couplings 311, 313 and 321 are speed-responsive type limit slip differentials in which the differential restriction power becomes large as the differential rotation speed becomes large. Also, the multiple disc clutches 315 and 317 are torque-responsive type limit slip differentials which are clamped by a reaction force in the action of differential gear mechanisms 307 and 309.
Furthermore, the differential gear mechanism 319 obtains the differential restriction function of the torque-responsive type by the torque transfer loss caused by the friction of the acting portion of the worm gear.
The multiple disc clutch 315 of the differential gear 301 is a S-H type differential gear (S: shaft, H: housing) arranged between a hub 323 on the shaft side and a differential gear case 325 (housing). And the viscous coupling 311 is a S-S type coupling arranged between hubs 323 and 327 on the shaft side. And each of the multiple disc cluch 317 and the viscous coupling 313 of the differential gear 303, and the viscous coupling 321 of the driving force transmission device 305 is S-H type.
In the case where the differential restriction mechanism is arranged in S-S, even if either wheel on the shaft side (on the side of a side gear) runs idle, uniform differential restriction force can be obtained. In the case of S-H arrangement, however, since the direction of the differential rotation is reversed by the differential gear mechanism to decrease the differential rotation number which is input to the limit slip differential, when the differential movement is input to the differential restriction mechanism via the differential gear mechanism due to the racing of the wheel on the one side, the wheel on the other side runs idle, and the differential restriction force becomes smaller than in the case where the differential movement is input directly to the limit slip differential. Therefore, there is caused a difference in the differential restriction force by the fact which wheel runs idle, and the differential restriction property becomes unequal.
As described above, in the differential gear 303, both of the limit slip differential of the speed-responsive type (viscous coupling 313) and the differential restriction mechanism of the torque-responsive type (multiple disc clutch 317) are the S-H type. In the differential gear 301, the differential restriction mechanism of the torque-responsive type (multiple disc clutch 315) is also the S-H type, and in the driving force transmission device 305, the differential restriction mechanism of the speed-responsive type (viscous coupling 321) is the S-H type. Thus, there has conventionally been no differential gear having uniform differential restriction property in combination with the differential restriction function of the speed-responsive type and the differential restriction function of the torque-sensitive type.
Furthermore, in order to arrange the viscous coupling 311 in S-S in the differential gear 301, the one shaft 329 has to be made longer than the other shaft 331, which makes the length of the two shafts unequal.
Furthermore, in the differential gear 301, since a stepped portion 333 is formed in the hub 327, there is a case where a differential gear to be incorporated cannot be incorporated due to the size or the shape of the differential gear case. Accordingly, the materialization is restricted, thereby the differential gear is not adaptable in the wide range to various types of vehicles.